A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis

Karen L. Baab, Peter Brown, Dean Falk, Joan T. Richtsmeier, Charles F. Hildebolt, Kirk Smith, William Jungers

Research output: Contribution to journalArticle

Abstract

The Liang Bua hominins from Flores, Indonesia, have been the subject of intense scrutiny and debate since their initial description and classification in 2004. These remains have been assigned to a new species, Homo floresiensis, with the partial skeleton LB1 as the type specimen. The Liang Bua hominins are notable for their short stature, small endocranial volume, and many features that appear phylogenetically primitive relative to modern humans, despite their late Pleistocene age. Recently, some workers suggested that the remains represent members of a small-bodied island population of modern Austro-Melanesian humans, with LB1 exhibiting clinical signs of Down syndrome. Many classic Down syndrome signs are soft tissue features that could not be assessed in skeletal remains. Moreover, a definitive diagnosis of Down syndrome can only be made by genetic analysis as the phenotypes associated with Down syndrome are variable. Most features that contribute to the Down syndrome phenotype are not restricted to Down syndrome but are seen in other chromosomal disorders and in the general population. Nevertheless, we re-evaluated the presence of those phenotypic features used to support this classification by comparing LB1 to samples of modern humans diagnosed with Down syndrome and euploid modern humans using comparative morphometric analyses. We present new data regarding neurocranial, brain, and symphyseal shape in Down syndrome, additional estimates of stature for LB1, and analyses of inter- and intralimb proportions. The presence of cranial sinuses is addressed using CT images of LB1. We found minimal congruence between the LB1 phenotype and clinical descriptions of Down syndrome. We present important differences between the phenotypes of LB1 and individuals with Down syndrome, and quantitative data that characterize LB1 as an outlier compared with Down syndrome and non-Down syndrome groups. Homo floresiensis remains a phenotypically unique, valid species with its roots in Plio-Pleistocene Homo taxa.

Original languageEnglish (US)
Article numbere0155731
JournalPLoS One
Volume11
Issue number6
DOIs
StatePublished - Jun 1 2016
Externally publishedYes

Fingerprint

Down syndrome
Hominidae
Homo
Down Syndrome
type collections
Brain
Tissue
Phenotype
phenotype
Indonesia
Cranial Sinuses
Chromosome Disorders
taxonomy
chromosome aberrations
sinuses
Islands
Skeleton
Population
skeleton
genetic techniques and protocols

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Baab, K. L., Brown, P., Falk, D., Richtsmeier, J. T., Hildebolt, C. F., Smith, K., & Jungers, W. (2016). A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis. PLoS One, 11(6), [e0155731]. https://doi.org/10.1371/journal.pone.0155731

A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis. / Baab, Karen L.; Brown, Peter; Falk, Dean; Richtsmeier, Joan T.; Hildebolt, Charles F.; Smith, Kirk; Jungers, William.

In: PLoS One, Vol. 11, No. 6, e0155731, 01.06.2016.

Research output: Contribution to journalArticle

Baab, KL, Brown, P, Falk, D, Richtsmeier, JT, Hildebolt, CF, Smith, K & Jungers, W 2016, 'A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis', PLoS One, vol. 11, no. 6, e0155731. https://doi.org/10.1371/journal.pone.0155731
Baab KL, Brown P, Falk D, Richtsmeier JT, Hildebolt CF, Smith K et al. A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis. PLoS One. 2016 Jun 1;11(6). e0155731. https://doi.org/10.1371/journal.pone.0155731
Baab, Karen L. ; Brown, Peter ; Falk, Dean ; Richtsmeier, Joan T. ; Hildebolt, Charles F. ; Smith, Kirk ; Jungers, William. / A critical evaluation of the down syndrome diagnosis for LB1, type specimen of Homo floresiensis. In: PLoS One. 2016 ; Vol. 11, No. 6.
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